Television system



July 1, 1930.

SEW-M2 W. H. WHITTEN, JR., ET AL TELEVISION SYSTEM Fi led June 25. 1927 a w y 0 m m m7 M V. 0 fia mfi v W 1 Wd m m l 7 ATTORNEY' ivaeam ND'OR mass:

Patented July 1, 1930 UNITED STATES PATENT OFFICE" WILLIAM H. WIIITTEN, an, or PITTSBURGH, AND TnAnnnus'n. GOLDSBOROUGH, or

lumination ofa light-sensitive device.

WILKINSBURG, PENNSYLVANIA, ASSIGNORS TO WESTINGHOUS E ELECTRIC AJ .\TD

MANUFACTURING COMPANY, A ooRI'oRATIoNor PENNSYLVANIA TnLEvIsIoN SYSTEM Application filed June 25,

This invention relates to systems for producing images of pictures or other objects at distances therefrom. It is applicable both to television systems and to systems for the transmission of pictures.

In the transmission of views, either of pictures or of actual objects, points in the view and in the reproduction thereof must be correlated and, at each point in the reproduction, an illumination must be produced corresponding to the intensity of light at the correlated point in the view. This requires the simultaneous control of three quantities, two for the two coordinates of the points and the .third for the intensity of the light. As this problem has ordinarily been attacked, each of these quantities is continuous. The quantities corresponding to the coordinates of the points must always be either absolutely continuous or vary by very small steps. It has heretofore been considered that the quantity corresponding to the brightness of each point must be capable of an indefinitely large number of different values, and so must vary through acontinuous range.

It is an object of this invention to provide a system for the transmission of views in which only a limited number of difierent degrees of illumination shall, be produced in the repro duction. I

It is a further object of this inventionto produce a view-transmission system in which the indefinitely large number of difieren't values of the intensity, of light at different points in the view shall be represented, in the output of the sending station, by an equally large number of values of the quantity representingthe'brightness but in which the receiving station shall represent the lightvalues by a relatively few number of values of the illumination in the reproduction of the view approximately corresponding to the brightness. e r

It is a further object of this invention to provide means for changing the frequency of an electrical oscillation in accordance with ik It is a further object of this invention to provide means whereby changes in the var ation frequency of a super-regenerative device 1927. Serial No. 201,315.

may be impressed upon the system without,

at the same time, impressing thereon the oscillation frequency of said super-regenerative device.

It is a further object of this invention toprovide a carrier-current system inwhich the points of a view' and. the homologous points in the reproduction are successively associated through the communication channel, and the intensity of light at the point in the view thus associated at any moment shall control the frequency of the modulation of the carrier current at that moment,

while the amplitude of said modulation remains constant.

It is a further object of this invention to provide a plurality of frequency-selective -devices by which the indefinitely large number of changes in the fre uency of the modula-- tion may be represent d by the selective action of said devices, one, or, at most two thereof, responding at any one moment.

It is a further object of this invention to provide means controlled by said selection of a frequency-responsive device for controlling the brightness of a light source.

It is a further object of this invention to provide a frequency-responsive device of a,

sufiiciently broad tuning to cause it to respond to a definite portion of the frequency range of said modulation.

In practicing our invention, we employ a super-regenerative vacuum-tube device. A device of this character produces oscillations of a relatively constant frequency but the oscillations are interrupted periodically at a frequency known as the variation frequency. The period of such interruptions is dependent upon, among other things, the value of the grid-leak resistance. By making a portion of the grid-lea sensitive to light, the variation frequency may be made to represent the light. We impress this variation frequency as a modulation upon a carrier-current system and the light is thus represented by the frequency of the modulation.

By receiving the modulated carrier wave upon an apparatus containing a number of frequency-responsive devices, each controlling the brightness of a light source, we ohtain a number of changes in intensity of the light which, although not forming a continuous gradation of light, can reproduce the picture satisfactorily.

5 or a more complete understanding of our th invention, reference is made to the followin in which,

Figure 1 is a apparatus at diagram of the circuits and the sending station, and diagram of the circuits and apparatus at the receiving statio he view to be in Fig. 1 by the arrow 1. a moving object, a stationary object or a picture of an object.

he optical system, including the lens 2 and prisms 3 and 4 and t e screen 5, is constructed in accordance with the dlSClOSlllB ill copendin I I l A t l 6 ll m0 St l. 1 .lm in mu g electric device 8. description and the accompanying drawings, 1;

The usual means for con tion frequency of the supe; vice comprise a grid condd h Va by a'grid-leak resistor 19. Ii a-tj e resistor 19 is in parallel wsh he variatioent i herefore, changes With the illunh t lf the device 8.

he vacuum-tube 21 is connected totube 23, in the usual to modulator, and the tube 23 th source 22 of plate-current ener pedance is provided in the lead from the positive side of the source 22 to t e common connection for the plates of the tubes 21 and 23.

he impedance COIIIPI'ISeS an m l 3 till in WI llllll ly coupled to three tuned circuits 55, 56 and v 57, each tuned to a different frequency. Three tuned circuits have been shown by way of illustration. The number of tuned circuits will be determined by the number of gradations of light required in'the reproduced picture. Obviously, the larger the number of said differently tuned circuits, the finer will be the gradations.

Each tuned circuit includes sufficient resistance to make it of broad tuning which may be a resistor 59 or the resistance of the inassigned to WVestinghouseElectric and Mandudtor or the losses in the condenser. Points of opposite potential in each of said tuned circuits are connected to opposed electrodes of a respective frequency-responsive relay 61 of the type described in the co-pending, joint application of A. M. Skellet and V. K. Zwory-. kin, filed January 3,- 1927, Serial No. 158,668,

ufacturing Company. Each of these relays includes a piezo-electric crystal 62 between said two electrodes. Each relay also includes a third electrode connected to the grid of an associated vacuum tube.

The potential impressed from the resonant circuits upon thefrequency-responsive relays is preferably supplemented by a source of direct-current potential. This is indicated upon the drawing by a battery .63 and a resistance connected thereto. The battery and resistance are shunted about a condenser'64 by means of which the alternating potential from the resonant circuit is transmitted.

The first of the said tuned circuits is associated with a vacuum tube 7 0, the plate-filament connection of which is in shunt to a portion 71 of a resistor 72. The vacuum tube 7 3 associated with the-next tuned circuit has its plate-filament connection in shunt to a portion of the resistor 72, including the portion 71' and an additionalportion. 74/ -The vacuum tube 75, associated with the third of said tuned circuits, has its plate-filament connection in shunt with the whole of said resistor 72.

' The resistor 72 is in serie'swith a light source 76 which is, preferably,.of the neon glow-tube type, although any light source which is responsive to potential changes, giving a corresponding intensity for each impressed potential, is suitable. The resistor 72 and light source 76 in-series are supplied ment.

fgom a high-potential direct-current source Instead of the usual three-electrode highvacuum tubes illustrated at 70, 73 and 75, it

is also contemplated that grid-controlled glow-discharge tubes, such' as are disclosed in the application of D. D. Knowles, filed November 19, 1926, Serial No. 149,290,'as-

signed to Westinghouse Electric and Manufacturing Company, may be used.- When such glow-discharge tubes are used, instead of the direct-current source 77, an alternating-current source should be supplied.

'Moreover, the frequency of said alternatingcurrent source should be at least as high as, and preferably higher than, would correspond to the shortest period during which-the lightis expected to continue at any one intensity.

The light from the source 76 impinges upon a screen. 81, preferably supplied with an ori-' fice 82, which constitutes practically a oint source of light.. If desired, instead 0 the orifice 82 .being completely transparent, it

may be filled with translucent material of such anoptical density that the light which passes through it at the time when all of the resistor 7 2 is present in the circuit of the light source 76 will be insuflicient to affect a photographic plate or be visible upon a screen in the receiving device. w

The receiving device comprises any desired system for optically associating the point-source 8 2 oflight'at any moment with 'that pointin the reproduction which correspondsto the point in the image 6 of the ob ject 1 in register with the orifice 7 at that mo-' Preferably, v the reproducing optical system is of the same type as the optical system at the sending station and, consequently, two rotating prisms 83 and 84 and a lens 85 are shown on the drawing.

The-screen 8'6, cooperating with the optical system, is intended to represent either the ground glass in a receiver of the camera type, the wall or screen in a moving picture exhibition hall, a photographic plate or any other suitable or known reproduction surface.

In the operation of the device, the-image of theview 1 is produced upon the screen 5 and moved over the'screen. The motion is such that the points of the image come, in 'turn,

intov registry with the hole 7. Preferably, this is accomplished by rotating the two prisms 3 and 4, one at a somewhat greater speed than the other.

I When the two prisms are in such relative position that their deflecting actions add, the

edge of the image is near'the hole. When the prisms are in such relative position that defleeting actions cancel, the central part of the image is in registry with'the hole. The trace of the hole upon the image is thus a spiral extending from the outside to the center and then from the center to thepgtside. 'lhe sev- I;

eral repetitions ofthe spiral are not in exact registry with one another. Consequently,

every point of the image is brought into regin synchronism with the optical system in Fig. 1 by any suitable or well-known means; for example, the energy delivered from the sending station may have a peculiar modulation imparted to it each time that the moving optical system passes through a certain posi-. tion and such modulation may be caused to control the optical system at the receiving station, bringing it into said characteristic position each time that the peculiar modulation arrives.

The maintenance of synchronism between the two optical systems results in directing the light from the orifice 82 upon that point on the screen 86 which corresponds to the position of the orifice 7 in the image 6 at that moment. As the image moves over the screen 5, therefore, the spot of light moves over the screen 86, thus reproducing, upon the screen 86, the path which the orifice? traces in the lmage 6.

In orderto produce a picture of the view 1,

the spot of light moving on the screen 86 must so vary in intensity that at each moment the brightness of the spot on the screen 86 corresponds to the illumination of the photocell 8. It is not necessary, however, that this correspondence be a proportionality and, in the system here disclosed, instead of a proportionality, the spot upon the screen 86 will have one of a relatively small number of intensities, that one which corresponds most nearly to the brightness of the illumination of the photocell The tube 10 will produce oscillations of a frequency determined by the tuning of the circuit 16-17, but not continuously. Instead 5 frequency are of being continuous, these oscillations are in-- terrupted at the variation frequency. As the illuminationof the photocell 8 changes, the combined resistance of the photocell and the resistor 19 in parallel changes, with the result that the super-regenerative device changes its variation frequency.

In order to ensure that the oscillations shall reestablish themselves promptly after each interruption, the coupling between the feedback coil 14 and the grid-coil 16 must be close enough to give to the device a strong tendency to oscillate.

The oscillations produced in the tube 10 pass readily through the condenser 15. They are prevented from passing through the bat- .tery 11 by the radio-frequency choke coil 12.

Currents or potential changes of the variation prevented from passing through the battery 11 by the iron-cored choke coil 13. Although this choke coil is shown asprovided with an iron core, it is 0nd. A satisfactory degree of detail can be. 7

obtained in television reproduction by a variation frequency of several hundred thousand cycles per second. The oscillations generated by the tube 10 must be higher than this in order that the variation period may contain a sufficient number of oscillation cycles for the action to be positive and dependable.

The average value of the plate current is increased when the tube is delivering oscillations and diminished when it is not. Consequently, the potential across the condenser 15 has a periodic change at the variation frequency in addition to the oscillations generated at the higher frequency.

The coupling between the tube 10 and the tube 21 may be a transformer of moderately broad tuning. It should transmit readily the (changeable) variation frequency, but should not transmit the oscillations generated by the tube 10 and, of course, would not transmit direct current. If, instead of such transformer, the coupling illustrated in Fig. 1 is used, the tuned circuit 3132 prevents the transmission of the oscillation frequency but will permit the transmission of the variation frequency.

The condenser 33 is of suflicient capacity to readily transmit the variation frequency. The condenser 15, by affording a path of low impedance for the oscillation frequency, increases the effectiveness of the tuned circuit 3132 in preventing the oscillation frequency from reaching the tube 21. The condenser 15 is of such small capacity as to present a large reactance to the variation frequency, whereby a large potential difference of this frequency is available to be transferred by the coupling.

The tube 21 acts as an amplifier for, the variation frequency and also as a modulator for the tube 23. The circuit 2425 should present a large impedance to the variation. frequency, in order that the most effective modulation may be obtained. The maximum impedance would be obtained by, a circuit which was sharply tuned to the variation frequency, but, as the, variation frequency changes throughout a substantial range and the impedance of the circuit 24-25 must be large over all of this range, the tuning of this circuitis broadened by the introduction of.

the resistance 26. v

Oscillations generated'by the tube 23 are prevented from'reaching the battery 22 by the radio-frequency choke coil '27. Prefer ably, these oscillations are of afrequency corresponding to some or 3.0 meters wave length, because radiation of this wave length obtains very certain control over great distanc'es.

The wave length chosen, whether it-is as short as stated or not, should be short enough for a suflicient number of cycles of the carrier frequency to be included within one cycle of the variation frequency. It'is preferable, but not necessary, that the carrier frequency differ substantially from the frequency of the oscillations generated in the tube 10.

Theoscillations generated in the tube 23 are modulated by the action of the tube 21,

d as is well understood by those skilled in the art. The output circuit of the tube 23 includes the usual tuned circuit 37 for storing the energy and. the usual reactive connection to the antennaby means of which the storedenergy may be radiated.

-The radiated energy is received upon the antenna 50 which is coupled to the circuit 51,

tuned to the carrier frequency. The received energy, after being amplified, ifnecessary, is impressed upon the detectortube 52 and the pptput current thereof includes the modula- 10I1S.

Although the drawing and the specific description disclose only the apparatus which is responsive to the modulations controlled by' the brilliancy of the several points in the view, other modulations, for purposes incicircuit 55 is in the lowest portion of this frequency range. The tuned circuits may, however, be arranged in any desired order.

When a bright portion of the image 6 is in registry with the orifice '7, the photocell 8 is brightly illuminated. It, therefore, becomes conductive. The combined resistance of the photocell and the resistor 19 is low, andthe variation frequency will, therefore, be high. The corresponding frequency in the output of the detector tube 52 will be high and will, therefore, come within the range to which the circuit 57 is responsive. The inclusion of the resistor 59 in this circuit, by broadening the tuning, will cause it to'be responsive not only to one maximum illumination of the photo cell 8 but to all illuminations from the most intense down to a certain limit. Thus, all portions of the view at which the light-intensity is strong are-correlated to the-circuit 57.

The battery 63 impressesacross the crystal 62 a potential which is less than the ionizing potential of the gas in the tube 61. When the circuit 57 is responding to a frequency within its range, an additional potential is impressed across the crystal 62 which, with the potential from the battery 63, is suflicient to cause the tube 61 to become operative. The range throughout which the response will occur is thus enlarged by the effect of the battery. It is preferable that the range of frequency over which any one tube, 73, for

example, is responsive shallslightly overlap the ranges for the neighboring tubes, 7 O and 75, in the example chosen.

When this occurs in the with the circuit 57, the tube7 5 becomes operative, with the consequence that the whole of the resistor 72 is short-'circuited and the full potential of the source 77 is impressed tube 61 associated upon the lamp 76. The couplin'g 57 is eifec tive at the highest portion of the frequency range; It, therefore, responds when the hotocell 8 is most brightly illuminated. onsequently, the light source 76 is brightest 'when the brightest portion of the image is in registry with the orifice 7. I

In the same way, when a portion of the image 6 of intermediate brightness is inregistry with the orifice 7, the illumination of the photocell 8 is intermediate, its'conductivity is therefore intermediate, the variation frequency of the super-regenerative device will be intermediate, and the tuned circuit which will respondis the intermediate circuit 56. The tube 73 will, therefore, become conductive, and a portion of the resistor 72 will be short-circuited, with the result that the light from the source-76 will be of an intermediate intensity.

When a dimly illuminated portion of the view 1 is optically associated with the orifice 7, the photocell 8 will be dimly illuminated, the variation frequency will, therefore, be slow and, the circuit 55 will respond. The

.tube 70 will then be conductive, and only the small portion 71 of the resistor 72 will be shunted. The light from the source 76 will, therefore, be 'dim, and the portion of the screen 86 corresponding to the portion of the image now in registry with the orifice 7 will be dimly lighted.

When a very dim or a perfectly dark portion of the image 6 is in registry with the orifice 7, the photocell 8 will be non-conductive; the variatlon frequency of the super-regenerative tube will be determined by the resistor 19; the modulation in the output will be slow, and the frequency in the plate circuit of the tube 52 will be too low for even the circuit 55' to be responsive thereto. Consequently, no part of the resistor 72 will be short-circuited, and the lamp 76 will either shine so dimly that a barely perceptible result is present upon the screen 86, or, if the lamp 76, under' these circumstances, is too dim to' penetrate the translucent medium in the orifice 82, the corresponding portion on the screen 86 may be completely dark.

The correspondence between the brilliancy in the image 6 and that in the image upon the screen 86 may, if desired, be reversed by re versing the order of the connections between the several tubes 61 and the corresponding portions of the resistor 72. This is of use when the screen 86, instead of being adapted for direct viewing, is a photographic plate and it is desired to produce a positive instead of a negative upon the developed plate.

Although I have described the gradations in light upon the screen 86 as consisting of a high, intermediate, low and very low intensity, a greater number of degrees of variation may be supplied by providing a larger number of tuned circuits, more sharply tuned, and a corresponding number of tubes whlch each shunt a ortion of the resistor 72.

When the light impressed upon the orifice 7 is of an intensity which falls between two of the degrees of intensity provided for' upon the screen 86, it may eifect two of the tuned circuits and cause two of the tubes 61 to become conductive. No disadvantage results from this because, if, for example, the tubes 73 and 75 are both. conductive at the same time,

' the fact that the tube 73 shunts a portion of ple, as the simultaneous transmission of sound with the picture.

It will also be apparent that the variation in brightness 'in the reproduced picture n this system is not affected by fading, because the brightness is dependent not upon the intensity but upon the frequency of the modu lation.

It will also be apparent that the apparatus does not require any very great exactness of adjustment. 'If,'from any accident, theaverage variation frequency of the tube 10 changes, the tuned circuits at the receiving station may beadjusted to correspond.- If:

. this adjustment should be so inexact that the correspondence between each tuned circuit and the light intensity for which it .was intended is destroyed, the result is only that the general tone of the reproduced pictu re is changed by one step to a brighter or a dimture is not altered, except at the ends of the range.

Although we have illustrated only a single form of our invention, and have indicated only a few possible modifications in the (lescription, many other modifications will readily occur to'those-skilled in the art. We, therefore, do not intend any limitation, except what is indicated in the claims or required by the prior art.

lVe claim as our invention:

1. In a system for the transmission of visual images, means for transmitting a carrier wave continuously modulated in accordance with the Varying illumination of said image, and means wherebys'aid illumination is reproduced in discontinuous steps at the receiving end.

2. In a view-transmission system, a highfrequency oscillation generator, a super -regenerative vacuum-tube device, means con: trolled by illumination for altering the variation frequency of said device, means for impressing on said high-frequency oscillations a modulation having a frequency equal to said variation frequency and a device responsive to said modulation in accordance with the frequency thereof.

. 3. In a view-transmission system, a big frequency oscillation generator, a super-regenerative vacuum-tube device, means controlled by illumination for altering the variation frequency of said device, means for impressing'on said high-frequency oscillations a modulation having a frequency equal to said variation frequency and a plurality of frequency-selective responsive devices together covering the frequency range of said modulation.

4.. In a view-transmission system, a highfrequency oscillation generator, 9. super-regenerative vacuum-tube device, means controlled by illumination for altering the variation frequency of said device, means for impressing on said high-frequency oscillations a modulation havinga frequency equal to said variation frequency and a plurality of frequency-selective responsive devices together covering the frequency range of said modulation, and a light-source controlled by said devices.

5. In a-view-transmission system, a sending device comprising means for producinghigh-frequency energy modulated by a modulation of varying frequency, illuminationcontrolled means forcontrolling the fre quency of said modulation, a receiving device comprising a plurality of frequencyselectlve devices each responsive to a range of frequencies overlapping the range of the next, the combined range of said devices covering the whole range of said modulation and a light-source the intensity of which is controlled by said devices.

6. In a View-transmission system, a sending station comprising means for delivering high-frequency energy modulated at a frequency corresponding to illumination, and a receiving station comprising a light-source having a brilliancy corresponding to the potential impressed thereon, a plurality of differently tuned frequency-responsive devices, means controlled thereby for impressing respectively different potentials on said lightsource and means for delivering to said tuned devices energy of a frequency determined by said modulation, whereby the brilliancy of said light-source will be determined by said illumination.

In testimony whereof, we have hereunto subgcribed our names this 22nd day of June, 192

WILLIAM H. WHITTEN, JR. THADDEUS R. GOLDSBOROUGH'. 

